The present invention generally relates to a hydraulically operating actuating device for a lift valve; and more particularly to a simplified actuating device, as compared to previously used actuating devices, which operates with a greatly reduced expenditure of energy.
An actuating device for a light valve is disclosed by German Published Unexamined Patent Application (DE-OS) No. 3,347,533. In the case of this actuating device, working fluid displaced from a cylinder by a piston during the movement of the lift valve is not used for performing work, with the result that energy generated by this movement is lost. This results in a very high energy requirement for actuation of the lift valve. Although it is stated in the above-referenced patent application that, for the purpose of energy recover, one side of the piston should alternately act as pump, it is not explained how this energy recovery should actually be carried out. Furthermore, in this actuating device an expensive control device is present, but this does not permit mutually independent control of different lift valves.
Accordingly, an object on which the invention is based is to operate a simplified actuating device, as compared to previously used actuating devices, with a greatly reduced expenditure of energy.
In the case of the actuating device designed in accordance with one advantageous embodiment of the present invention, the actuation movement of a piston associated with a lift valve is initiated by springs, which, in end positions, are stressed to differing degrees, a working fluid, which is under pressure, being pushed from one stroke space into the other. The potential energy stored in the springs at end positions of the piston are thus used for accelerating the piston and the lift valve and are recovered during braking. In addition, the energy of the working fluid is not lost during its expulsion from the stroke space, and therefore, the supply of energy from outside can be restricted to the replacement of energy losses, in particular frictional losses, while the energy required for accelerations is provided by energy recovery. A further advantage is produced in that the energy recovering braking of the piston and of the lift valve damps their movement and prevents a hard impact at the end position.
An arrangement and prestressing of the springs which is space saving and advantageous for the actuation movements of the lift valve is also provided.
According to advantageous features of preferred embodiments of the present invention, an energy saving control device is provided for the actuating device, with the aid of which each individual actuation movement of the lift valve is initiated, so that each of these actuation movements can be altered and matched to requirements.
Additionally, energy losses caused by mechanical and hydraulic friction can be replaced in a simple and inexpensive manner by feeding working fluid which is under pressure from the pressure source into a stroke space towards the end of a stroke movement, provision being made for a simultaneous removal of an identical quantity of working fluid from the other stroke space. As a result, only a small portion of the working fluid to be delivered into or out of a stroke space upon each stroke movement has to be delivered by the pressure source with the expenditure of energy.
Further, the arrangement and control of the outlet openings is particularly simple.
A considerable acceleration of the stroke movement of the lift valve in the opening direction can be achieved by means of the design of the actuating device according to further embodiments of the present invention, although some of the energy recovery has to be sacrificed.
Also, a simple and reliable device which brings the lift valve into a starting position necessary for normal operation is envisioned when the internal combustion engine is started.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.